Aquaculture, 69 (1988) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFED 1-14 1 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands The Association between Virulence and Cell Surface Characteristics of zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ Aeromonus saZmonicida ALEXANDRA ADAMS, ANDREA BUNDY, KIM THOMPSON and M.T. HORNE Aquatic Vaccine Unit, Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA (Great Britain) (Accepted ‘3November 1987 ) ABSTRACT Adams, A., Bundy, A., Thompson, K. and Horne, M.T., 1988. The association between virulence and cell surface characteristics of Aeromonas salmonicida. Aquaculture, 69: 1-14. Two virulent strains of Aeromonas salmonicida were shown to lose their capacity for causing furunculosis in rainbow trout (Salmo gairdneri Richardson) following serial subculture on agar. Strain MT004 (A-layer negative, non-autogglutinating, protease positive) ceased to produce ex- tracellular products (ECP) soon after subculturing, while the other strain, 184/86 (A-layer po- sitive, autoagglutinating, protease negative), retained the A-layer, but the synthesis of another protein in the outer membrane, termed the PO protein, appeared to be inhibited. Strains 184/86, MT004 (both virulent) and five other strains (all avirulent) were characterised with regard to their surface properties. All autoagglutinating strains (184/86, B85016 and P - 480) were A-layer positive (using a monoclonal antibody probe), while all non-agglutinating strains (B85016, P + 480,1102 and MT004) were A-layer negative. Strain 8060, previously characterised by other workers as A-layer negative but autoagglutinating was found to be A-layer positive. These results illustrate that the virulence mechanism of Aeromonas salmonicidais complex and appears to vary between strains. INTRODUCTION zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA The virulence mechanisms of zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM Aeromonas salmonicida have been investi- gated by many workers. There is much evidence for the involvement of extra- cellular proteases and cytolysins in virulence (Fuller et al., 1977; Sakai, 1977; Munro et al., 1980; Cipriano et al., 1981; Ellis et al., 1981). In addition, Kay et al. (1981) demonstrated the importance of the additional protein layer (A- protein) on the surface of Aeromonas salmonicida. The surface of many bac- teria has been shown to be of key importance in pathogenicity (Trust et al., 1982). The initial stage of infection and colonisation of an animal host by numerous bacteria is attachment to the epithelial surface (Arbuthnott and Smyth, 1979). Most virulent strains of Aeromonas salmonicida possess an A- 0044-8486/88/$03.50 0 1988 Elsevier Science Publishers B.V.